One example of an application for the apparatus of the present invention is highwall mining. During the past forty years, highwall mining has proven to be an efficient method of mining coal, or other sought after material, that would not be mined by other methods. Highwall mining is a form of mining frequently used to supplement strip mining.
Strip mining is used when the sought after material deposits, such as coal, occur relatively close to the surface. In strip mining, the top several layers of earth over a coal deposit are removed along with the coal deposit to gain access to the coal deposit. The material of the covering layers is called overburden. When the coal to overburden ratio falls below a certain ratio, the process becomes unprofitable and strip mining ceases to be the economically preferred technique at that location. At that point in time, the strip mining has produced a large pit with seams of coal extending from the surface of the walls of the pit back into the earth. Highwall mining is a type of mining used to extract, or mine, the coal in the seams terminating at the walls of the pit.
In highwall mining, a highwall mining machine is located on the pit floor in alignment with a coal seam and a remote operated cutter module is forced into the coal seam. The cutter cuts a series of parallel rectangular cuts back into the seam up to 1,000 feet from the face of the wall. This is considered too dangerous for the insertion of any personnel and the cutter modules are directed and operated remotely. The coal mined by the cutter module is transported from the cutter module to the surface area by augers or conveyor belt systems.
Typically, the cuts and the entries to the cuts are rectangular. The width of the entry to a cut is dependent on the type of cutter module used, and the width may vary from 9½ feet to 12 feet. The height of the entry is more dependent on the coal seam's thickness, and the height may vary from 28 inches to more than 15 ft.
Today's highwall miners produce an average of 100,000 tons of coal per month per highwall miner. Highwall miners and their supporting augers and conveyors are highly automated. Due to the cutter module design as well as other factors in the mining process, some percentage of the coal mined by the highwall miner ends up as spillage and is not recovered. The percentage of spillage is estimated, conservatively, to be between eight and fifteen percent of the coal that is cut during the mining cycle. This coal remains in the cut after the cutter module and the support augers or conveyors have been extracted.
On occasions, components from the cutter modules become detached and are lost during the mining process. At the present time, there is not a practical way of recovering these components, and the cutter module cannot continue to operate with the loose component in the cut. When this happens, the only option for the operator is to withdraw the mining equipment from that particular cut, or hole, and proceed to the next setup. The component from the cutter module is lost, as well as any recoverable coal remaining in the seam past the lost component.
At present time, it is estimated that there are more than one hundred highwall miners being operated in the coal industry, each one producing multiple cuts during an operating day. They all have the same problems to varying degrees. A need exists for a system capable of recovering mined coal that is left behind in highwall mining cuts as well as lost components. Substantial monetary gains may be achieved by recovering the coal and lost components. Additionally, once a component is recovered and the cut cleared, a highwall miner can return to the cut to further exploit the seams at that location for further monetary benefit. For monetary purposes the system must be efficient, reliable, and not labor intensive. For safety purposes, the system must not require personnel to be exposed at or near the highwall of the pit. The system should be able to work in close proximity with high wall miners.